1. Field of the Invention
The present invention relates to cassette handling systems and, more particularly, to automated cassette handling systems for magnetic-medium cassettes or the like with high reliability.
2. Description of Related Art
Tape library systems are used to store large amounts of data on tape. They may be employed in a hierarchial storage management system, such as a concurrent backup system for data stored on hard disk drives in a computer system or as a data library for access by a computer system. While many personal computers today store up to 500 megabytes or more on hard disk, tape library systems are able to store 50 to 500 times as much data, with some systems yielding capacities over one terabyte (one million megabytes).
A primary concern to a user of tape library systems is reliability. As many customers such as banks, airlines, government agencies, and so on rely on tape library systems for storing and accessing data, it is critical that the library system does not malfunction, preventing a user from accessing information stored in the system. Furthermore, speed is also essential in the desirability of a system.
A typical tape library system for storing a number of tapes or cartridges on which data are stored magnetically has a storage unit for storing the tapes and a number of tape drives for reading or writing data. One known cassette or cartridge rack for magnetic tapes is disclosed in U.S. Pat. No. 5,103,986, granted to C. P. Marlowe on Apr. 14, 1992. A control system, which has an interface with a computer, transports the tapes from the storage unit to one of the tape drives and vice versa, which is called an exchange. The control system includes electromechanical apparatus which moves within the library system. As is true with any electromechanical process or movement, the accuracy and reliability of the process relies upon the precision of the movement and the associated tolerances. Therefore, in order to maximize the number of exchanges which are accomplished without any malfunction of the system, the precision of the process should be maximized, while of course taking into consideration cost-effectiveness and other related factors. Collateral factors which deserve consideration include speed of operation and compactness of the system.
Accordingly, principal objects of the present invention are to increase the precision of cassette handling systems, to increase reliability and/or compactness of such systems, and to operate the systems at high speed compatible with electromechanical reliability.
SUMMARY OF THE INVENTION
A cassette handling system according to an exemplary embodiment of the present invention stores a plurality of cassettes in storage units and transports one of the cassettes from one of the storage units on a carrier assembly to a tape drive unit, or vice versa. Prior to inserting the cassette into one of the units, the position of the cassette is accurately positioned with respect to the unit into which it is being inserted by repositioning the cassette on a reference platen. The reference platen defines a position from which the cassettes are insertable into the units without obstruction. Accordingly, the cassette handling system has a high reliability in that the number of transportation sequences or exchanges without malfunction is increased. Furthermore, the cassette handling system may store cassettes with increased density as the cassettes are precisely transported throughout the system, requiring less space between individually stored cassettes.
More specifically, the cassette handling system generally includes the carrier assembly with the reference platen positioned thereon and an engaging assembly with a pair of couplers for engaging a cassette. A control unit actuates various motors to displace the carrier assembly between the storage and tape drive units, to extract and insert the respectively from and into the units, and to reposition the cassette being transported accurately.
In operation, the carrier assembly is displaced to a unit in which a desired cassette is received. The cassette is engaged by the couplers and extracted from the unit. The cassette is engaged by the engaging assembly above the reference platen. The carrier assembly is then displaced to a vacant unit. Before the cassette is inserted into the unit, the couplers disengage the cassette onto the reference platen and re-engage the cassette while it is positioned on the reference platen. The cassette is then inserted into the desired unit.
By repositioning the cassette, any uncertainty in the movement of the carrier assembly to one of the units from which a cassette is to be extracted is substantially eliminated, such that the cassette is insertable into another one of the units without failure due to this uncertainty. Considering this procedure from another aspect, when the mechanical couplers engage the cassette to extract it from a first unit, there is a first tolerance or possibility for slight displacement between the carrier assembly and the first unit, so that the cassette may be gripped and held in a location slightly displaced from the optimum position relative to the carrier. Similarly, there is a second tolerance or possibility that the receiving slot may not be aligned with the optimum carrier alignment position. By the use of the reference platen, any uncertainty due to these tolerances is essentially eliminated, as the insertion is always accomplished from the same position relative to the carrier. Also, by accurately positioning the cartridge immediately before inserting it into a unit, any possible undesired shifting of the cartridge in the couplers as a result of external vibration or the like, in the course of carrier movement, is eliminated.
In order to additionally improve the reliability of the cassette handling system according to the present invention, vibration within the carrier assembly is substantially reduced or eliminated. The carrier assembly is shifted or displaced between the units by means of a drive collar received on a threaded shaft. A carrier motor rotates the drive collar about the shaft, thereby displacing the carrier assembly. The shaft might potentially vibrate as a result of various forces caused by the rotation of the drive collar thereabout, or by environmental vibration. Therefore, a plurality of compression springs are disposed at one of the ends of the threaded shaft to increase the axial tension on the shaft to raise the resonant frequency and to preclude or damp the potential vibration thereof so that the carrier assembly moves between the units smoothly and precisely.
Additional aspects and advantages of the present invention will become apparent to one skilled in the art from the following detailed description and illustrative accompanying drawings. As will be realized, the invention is capable of other embodiments and of modifications in various respects without departing from the scope of the invention.